#14509: feat: setup and configure proxy system

Set up and configure the proxy system. Fixed rotation bug and added default config. All tests passing. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adds two new subsystems: - `proxy_system/` (Python): a proxy manager (`Proxy`, `ProxyManager`, config loader, CLI) plus a `ProxyScraper` that rotates proxies while scraping. - `unified_api/` (TypeScript/Express): a new API server skeleton with config parsing, middleware, controllers/services/routes, and a DB abstraction intended to support SQLite/Postgres. Overall direction is clear, but there are a few correctness issues in the new Unified API database layer/entrypoint and some dead code paths in the proxy scraper that should be fixed before merge. <h3>Confidence Score: 2/5</h3> - Not safe to merge as-is due to database initialization/runtime issues in the new unified_api server. - The PR introduces a new DB abstraction and schema initialization that will currently recurse during startup, uses invalid DDL (INDEX clauses inside CREATE TABLE), and has SQL placeholder incompatibilities with Postgres; these are runtime blockers for the new API. Proxy system changes are mostly self-contained but have at least one dead code path in contact-page scraping. - unified_api/src/models/database.ts, unified_api/src/index.ts, unified_api/src/services/jobs.service.ts, proxy_system/proxy_system/scraper.py <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->